Lighting device for display device and display device using the same

ABSTRACT

A backlight device includes a light guide plate opposed to fluorescent tubes, a diffusion sheet stacked on the light guide plate, and lens sheets further stacked on the diffusion sheet. A tip end of a corner portion of the diffusion sheet has a shape defined by removing a portion of the sheet along a straight line spanning between two sides constituting the corner portion. In first of the lens sheets, a tip end portion of a corner portion formed by two sides has a shape defined by removing a portion of the sheet in a larger amount than in the diffusion sheet by a circular arc which projects outward. In a second of the lens sheets, a tip end of a corner portion formed by two sides has a shape defined by removing a larger amount than in the first of the lens sheets along a straight line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lighting device for a display devicewhich is used for a liquid crystal panel or the like, and a displaydevice using the same.

2. Description of the Related Art

Japanese Patent Application Laid-Open No. 2004-125964 (FIG. 2) disclosesa prior art backlight device for a liquid crystal display. In thisbacklight device, a plurality of optical films are stacked on each otherand opposed to a housing portion of a light source such that lightemission from the light source is uniformly irradiated to a display.

A backlight device has to include the plurality of optical sheetswithout omitting any of the sheets in its assembled state. However, aplurality of optical sheets usually appear to have the same or similarthin sheet shapes, and when they are seen from above in a stacked state,they cannot be discriminated from one another. Therefore, it isdifficult to check for the presence of the plurality of optical sheetsin the device. Thus, in the backlight device according to the abovedescribed prior art, the corner portion of each of the optical sheets iscut off along a straight line, and the cutoff amounts are made to differin accordance with the respective sheets (the triangular shapes whichare cut off from the respective sheets have the same or similar shapesto one another). The sheet with the smallest cutoff amount is on thebottom, and the sheets with larger cutoff amounts are sequentiallystacked on top of one another. In this way, the cutoff portions are seenfrom above during the manufacturing process, so that the lack or absenceof one or more of the optical sheets in the assembly is detected.

However, an optical sheet must have a minimum predetermined surface areafor maintaining a light control function. Thus, the cutoff portion oneach optical sheet must be as small as possible. Accordingly, it isstill difficult to see the corner portions cut off along the straightlines and determine the absence of the optical sheets in themanufacturing process.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide a lighting device for a display devicein which the absence of one or more of a plurality of optical sheets canbe easily detected, and a display device including such a lightingdevice.

A lighting device for a display device according to a preferredembodiment of the present invention includes a plurality of opticalsheets each having corner portions and having a shape in which a tip endof the corner portion is removed along a line segment spanning betweentwo sides constituting the corner portion, and a sheet layered bodydisposed near a light source defined by the plurality of the opticalsheets being stacked on each other in an order of size of the remainingportions of the corner portions, the optical sheets having the largestremaining portion being the first in the stack or on the bottom of thestack, and wherein shapes of the line segments spanning betweenrespective two sides constituting the corner portions of adjacent onesof the plurality of the optical sheets differ from each other.

With such a unique structure, if any one of the optical sheets isabsent, the arrangement of the line segments differing in shape from oneanother becomes abnormal, and a sense of incompatibility the absence ofone or more of the optical sheets can be visually detected instantly.

Other features, elements, steps, characteristics and advantages of thepresent invention will be described below with reference to preferredembodiments thereof and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a liquid crystal displayaccording to a first preferred embodiment of the present invention.

FIG. 2A is a plane view showing the state before stacking of a sheetlayered body constituting the liquid crystal display shown in FIG. 1.

FIG. 2B is a plane view showing the stacked state of a sheet layeredbody shown in FIG. 2A.

FIG. 3A is a plane view showing the state before stacking of a sheetlayered body according to a second preferred embodiment of the presentinvention.

FIG. 3B is a plane view showing the stacked state of a sheet layeredbody shown in FIG. 3A.

FIG. 4A is a plane view showing the state before stacking of a sheetlayered body according to a third preferred embodiment 3.

FIG. 4B is a plane view showing the stacked state of a sheet layeredbody shown in FIG. 4A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First PreferredEmbodiment

A first preferred embodiment of the present invention will be describedwith reference to FIGS. 1, 2A and 2B. A liquid crystal display 1according to this preferred embodiment is a display device, andpreferably includes a backlight device 2, which is a lighting device fora display device, and a display panel 3, which is a display and isdisposed in front of the backlight device 2 and capable of displayingimages. The backlight device 2 preferably is a direct type backlightdevice including a tray 22 housing a plurality of fluorescent tubes 21,a light guide plate 23 made of a synthetic resin and disposed over thetray 22, a diffusion sheet 24 disposed on the light guide plate 23, andtwo lens sheets 25 and 26 further disposed on the diffusion sheet 24.However, the backlight device 2 is not limited to this configuration. Asshown in FIG. 1, the diffusion sheet 24 and the lens sheets 25 and 26are preferably optical sheets formed of a synthetic resin. Each of theoptical sheets preferably has a substantially rectangular shape in theplane view, and a sheet layered body is defined by the plurality ofoptical sheets stacked on each other.

As shown in FIG. 1, a reflective sheet 22 a is provided in the tray 22,and a plurality of fluorescent tubes 21 are located on the reflectivesheet 22 a. The respective fluorescent tubes 21 are disposed in parallelor substantially in parallel at equal or substantially equal spaces fromone another in the tray 22, and are arranged in a plane configuration asa whole. Meanwhile, the display panel 3 includes a pair of glass boards5 respectively fitted in frames 4, and a panel board 6 which is fittedbetween them and is constituted of a pair of transparent electrodes andan alignment layer containing liquid crystal.

As shown in FIG. 2A, each of the diffusion sheet 24 and the lens sheets25 and 26 preferably has a shape such that a tip end of a corner portionlocated at one of its four corners is removed by a line segment spanningbetween two sides constituting the corner portion, and the shapes of theline segments differ from each other between the adjacent sheets 24 and25, and between the adjacent sheets 25 and 26. Specifically, thediffusion sheet 24 preferably has a shape such that the tip end of thecorner portion formed by two sides 24 a and 24 b among its outer sidesis removed by a straight or substantially straight line 24 c connectingthe two sides 24 a and 24 b. The lens sheet 25 preferably has a shapesuch that the tip end of the corner portion formed by two sides 25 a and25 b is removed by a circular or substantially circular arc 25 cprojected outward and connecting the two sides 25 a and 25 b. The lenssheet 26 preferably has a shape such that the tip end of the cornerportion formed by two sides 26 a and 26 b is removed by a straight orsubstantially straight line 26 c connecting the two sides 26 a and 26 b.

The line segments 24 c and 26 c which remove the tip ends of the cornerportions of the sheets 24 and 26 are preferably arranged to define anangle of about 45° with respect to the outer sides 24 a and 24 b, and 26a and 26 b of the sheets 24 and 26. However, the line segments 24 c and26 c are not limited to this, and the circular or substantially circulararc 25 c which removes the tip end of the corner portion of the sheet 25is preferably formed by a quarter of the circumference of a circle witha predetermined radius. As shown in FIG. 2B, the diffusion sheet 24 andthe lens sheets 25 and 26 are stacked in the order of the size of theremoved portions, with the optical sheet having the smallest removedportion being the first sheet (in other words, they are stacked in theorder of the size of the remaining portion, the largest remainingportion being stacked first or on the bottom of the stack). The endportions of the circular or substantially circular arc 25 c of the lenssheet 25 are connected by the straight or substantially straight line 26c of the lens sheet 26 which is stacked on the lens sheet 25. The sheets24, and 26 may be formed by actually cutting the corner portions of thesheet members which originally have the substantially rectangular shapesby the straight or substantially straight lines 24 c and 26 c and thecircular or substantially circular arc 25 c, respectively, or the sheets24, 25 and 26 may be formed into the shapes in which the tip ends of therespective corner portions are originally removed by using molds.

According to this preferred embodiment, the shapes of the line segments24 c, 25 c and 26 c spanning between the two sides 24 a and 24 b, 25 aand 25 b, and 26 a and 26 b which constitute the corner portions of thediffusion sheet 24 and the lens sheets 25 and 26 differ from each otherbetween the adjacent sheets. Therefore, if any one of these sheets 24,25 and 26 which constitute the sheet layered body is absent, thearrangement of the line segments 24 c, 25 c and 26 c differing in shapesfrom each other becomes irregular, and a sense of incompatibility isinstantly visually detected. Therefore, the presence or absence of thesheets 24, 25 and 26 can be easily determined. Among the adjacentsheets, as for the one sheet 24 of the two adjacent sheets and the onesheet 26 of the two adjacent sheets, the two sides 24 a and 24 b, andthe two sides 26 a and 26 b, which constitute the corner portions, areconnected by the straight or substantially straight lines 24 c and 26 c,respectively. As for the other sheet 25, the two sides 25 a and 25 bconstituting the corner portion are connected by the curved line(circular or substantially circular arc 25 c), and thereby, the straightor substantially straight lines 24 c and 26 c are adjacent to the curvedline 25 c. Therefore, the absence of the sheets 24, 25 and 26 isdetected more easily.

The lens sheet 25 of which two sides 25 a and 25 b constituting thecorner portion are connected by the circular or substantially circulararc 25 c so as to project outward is stacked on the diffusion sheet 24of which two sides 24 a and 24 b constituting the corner portion areconnected by the straight or substantially straight line 24 c. The lenssheet 26 of which two sides 26 a and 26 b constituting the cornerportion are connected by the straight or substantially straight line 26c is further stacked on the lens sheet 25, and the straight orsubstantially straight line 26 c of the lens sheet 26 stacked on thelens sheet 25 is located at a position where the straight orsubstantially straight line 26 c connects the end portions of thecircular or substantially circular arc 25 c. Thereby, even when thethree sheets 24, 25 and 26 are laid on one another, the circular orsubstantially circular arc 25 c and the straight or substantiallystraight line 26 c do not overlap each other, and they can be clearlydiscriminated. The straight or substantially straight line 26 c is notlocated deeply inward away from the circular or substantially circulararc 25 c, and the removed width of the corner portion of the sheet 26located on the top is not large. Therefore, a compact and lightweightbacklight device 2 can be provided. Further, by disposing the displaypanel 3 in front of the backlight device 2, the liquid crystal display 1in which the presence or absence of the sheets 24, 25 and 26 can beeasily determined can be provided.

Second Preferred Embodiment

Next, a second preferred embodiment of the present invention will bedescribed with reference to FIGS. 3A and 3B. In this preferredembodiment, the lens sheet 25 preferably has a shape such that the tipend of the corner portion is removed by a straight or substantiallystraight line 25 d which connects the outer sides 25 a and 25 b andforms an angle of about 45° relative to the sides 25 a and 25 b, isstacked on the diffusion sheet 24 such that the tip end of the cornerportion is removed by a circular or substantially circular arc 24 dformed by a quarter of the circumference which connects the two sides 24a and 24 b constituting the corner portion and is projected outward.This preferred embodiment may be applied to the lens sheets 25 and 26.As shown in FIG. 3A, a length L in the diagonal direction of thestraight or substantially straight line 25 d of the lens sheet 25 islonger than a radius R of the circular or substantially circular arc 24d formed in the diffusion sheet 24, and the length of the straight orsubstantially straight line 25 d is longer than the length of theshortcut of the end portions of the circular or substantially circulararc 24 d (shown in FIG. 3B). In this preferred embodiment, the cornerportion of the lens sheet 26 which is stacked on the sheet 25 is cut bya circular or substantially circular arc or a straight or substantiallystraight line so as not to overlap the straight or substantiallystraight line 25 d. The sheets 24 and 25 may be formed by actuallycutting the corner portions of the sheet members which originally havethe substantially rectangular shapes by the circular or substantiallycircular arc 24 d and the straight or substantially straight line 25 d,respectively, or the sheets 24 and 25 may be formed into the shapes inwhich the tip ends of the respective corner portions are originallyremoved by using molds.

According to this preferred embodiment, the lens sheet 25 of which twosides 25 a and 25 b constituting the corner portion are connected by thestraight or substantially straight line 25 d is stacked on the diffusionsheet 24 of which two sides 24 a and 24 b constituting the cornerportion are connected by the circular or substantially circular arc 24 dso as to project outward, and the length of the straight orsubstantially straight line 25 d is larger than the length of theshortcut of the end portions of the circular or substantially circulararc 24 d. Therefore, in the adjacent sheets 24 and 25, the straight orsubstantially straight line 25 d and the circular or substantiallycircular arc 24 d do not overlap each other, and can be clearlydiscriminated, and therefore, the absence of the sheets 24 and 25 can bedetected more easily.

Third Preferred Embodiment

FIGS. 4A and 4B show a third preferred embodiment of the presentinvention. In this preferred embodiment, the lens sheet 25 preferablyhas a shape such that the tip end of the corner portion is removed by astraight or substantially straight line 25 e which connects the outersides 25 a and 25 b and defines an angle of about 45° with respect tothe sides 25 a and 25 b, is stacked on the diffusion sheet 24 such thatthe tip end of the corner portion is removed by a circular orsubstantially circular arc 24 e by a quarter of the circumference whichconnects the two sides 24 a and 24 b constituting the corner portion andis projected outward. Further, the lens sheet 26 preferably has a shapesuch that the tip end of the corner portion is removed by a circular orsubstantially circular arc 26 e (the radius is preferably the same asthat of the circular or substantially circular arc 24 e) by a quarter ofthe circumference which connects the two sides 26 a and 26 bconstituting the corner portion and is recessed inward is stacked on thelens sheet 25. As shown in FIG. 4B, in this preferred embodiment, thepositions of the end portions of the circular or substantially circulararcs 24 e and 26 e of the diffusion sheet 24 and the lens sheet 26correspond to each other, and the straight or substantially straightline 25 e of the lens sheet 25 is formed to connect these end portions.The sheets 24, 25 and 26 may be formed by actually cutting the cornerportions of the sheet members which originally has the substantiallyrectangular shapes, by the circular or substantially circular arcs 24 eand 26 e and the straight or substantially straight line 25 e,respectively, or the sheets 24, 25 and 26 may be formed into the shapeswith the tip ends of the respective corner portions originally removedby using molds.

According to this preferred embodiment, the lens sheet 25 of which twosides 25 a and 25 b constituting the corner portions are connected bythe straight or substantially straight line 25 e is stacked on thediffusion sheet 24 in which the two sides 24 a and 24 b constituting thecorner portion are connected by the circular or substantially circulararc 24 e to project outward. Further, the lens sheet 26 of which twosides 26 a and 26 b constituting the corner portion are connected by thecircular or substantially circular arc 26 e so as to recess inward isstacked on the lens sheet 25. The positions of the end portions of thecircular or substantially circular arcs 24 e and 26 e correspond to eachother, and the straight or substantially straight line 25 e is locatedat the position at which it connects these end portions. Thereby, in thecorner portions of the sheets 24, 25 and 26, the two circular orsubstantially circular arcs 24 e and 26 e and the straight orsubstantially straight line 25 e form one closed pattern, and therefore,the absence of the sheets 24, 25 and 26 can be easily detected at aglance.

Other Preferred Embodiments

The present invention is not limited to the preferred embodimentsdescribed above and illustrated in the drawings, but, for example, thefollowing preferred embodiments are also included in the technical scopeof the present invention.

The optical sheets in the lighting device for a display device accordingto various preferred embodiments of the present invention preferablyinclude all light adjusting sheets such as light guide plates, andreflective sheets.

The lighting device for a display device according to various preferredembodiments of the present invention is also applicable to a side lighttype.

Cold-cathode tubes, hot-cathode tubes, discharge lamps and the like areapplicable to the light source of the lighting device of a displaydevice according to various preferred embodiments of the presentinvention.

In the lighting device of a display device according to variouspreferred embodiments of the present invention, the curved lines otherthan a circular or substantially circular arc, or the straight orsubstantially straight lines other than that which defines an angle withrespect to the outer sides of the sheet being about 45° may be appliedto the line segment by which the corner portion is cut.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A lighting device for a display device, comprising: a plurality ofoptical sheets each having corner portions and each having a shape inwhich a tip end of one of the corner portions is removed along a linesegment spanning between two sides constituting said one of the cornerportions so as to produce a remaining portion; a sheet layered bodyincluding the plurality of optical sheets and through which light from alight source passes; wherein shapes of the line segments spanningbetween respective two sides constituting the corner portions ofadjacent ones of the plurality of optical sheets differ from each other.2. The lighting device for a display device according to claim 1,wherein one of the shapes of the line segments of one of the adjacentones of the plurality of optical sheets is a substantially straightline, and another of the shapes of the line segments of another of theadjacent ones of the plurality of optical sheets is a substantiallycurved line.
 3. The lighting device for a display device according toclaim 2, wherein said optical sheet having the line segment that is asubstantially straight line and said optical sheet having the linesegment that is a substantially curved line are arranged such that theline segments thereof are off from each other.
 4. The lighting devicefor a display device according to claim 2, wherein the remaining portionof the another of the adjacent ones of the plurality of optical sheetsis defined by the substantially curved line and projects outward beyondsaid optical sheet having the line segment that is a substantiallystraight line.
 5. The lighting device for a display device according toclaim 2, wherein the remaining portion of the one of the adjacent onesof the plurality of optical sheets is defined by the substantiallystraight line and projects outward beyond said optical sheet having theline segment that is a substantially curved line.
 6. The lighting devicefor a display device according to claim 2, wherein the remaining portionof the one of the adjacent ones of the plurality of optical sheets isdefined by the substantially straight line and projects outward beyondsaid optical sheet having the line segment that is a substantiallycurved line, and the remaining portion of the another of the adjacentones of the plurality of optical sheets is defined by the substantiallycurved line and projects outward beyond another of said optical sheetshaving the line segment that is a substantially straight line.
 7. Adisplay device, comprising: the lighting device for a display deviceaccording to claim 1; and a display disposed in front of the lightingdevice for a display device.